(1) Field of the Invention
The invention described herein relates to sonar systems and in particular to sonar signal detection and processing.
(2) Description of the Prior Art
Hull-mounted sonar systems typically include both active and passive systems and may have one or two transducers. Often a second transducer is used to produce low frequency, long range detection. The resolution achievable using hull-mounted transducers is relatively coarse. A target may, for example, provide an enlarged return (due to the lack of resolution) which thereby diminishes the accuracy of azimuth information and, to a lesser extent, the accuracy of range information. Further, small targets, such as submerged mines may be undetectable due to the lack of resolution. In an effort to improve resolution, towed arrays are often added to a ship's sonar system. Such a towed array can use the transmissions of the hull-mounted system for active operations, or transmissions from other sources for passive operations. A difficulty remaining with the towed array, however, is the requirement to stabilize the array during operation. This requirement means that the ship must maintain a relatively non-maneuvering course during sonar operations. Due primarily to the threat of torpedo attack, standard procedure is to sail a series of randomly-timed, zigzag courses, as a defensive measure. This procedure prevents stabilization of towed-array sonars, thereby creating a need for hull-mounted systems which can provide towed array capabilities.